Iridium-catalyzed C-C coupling via transfer hydrogenation: Carbonyl addition from the alcohol or aldehyde oxidation level employing 1,3-cyclohexadiene

Under hydrogen autotransfer conditions employing a catalyst derived from [Ir(cod)Cl](2) and BIPHEP, 1,3-cyclohexadiene (CHD) couples to benzylic alcohols 1a-9a to furnish carbonyl addition products 1c-9c, which appear as single diastereomers with variable quantities of regioisomeric adducts; 1d-9d. Under related transfer hydrogenation conditions employing isopropanol as terminal reductant, identical carbonyl adducts 1c-9c are obtained from the aldehyde oxidation level. Isotopic labeling studies corroborate a mechanism involving hydrogen donation from the reactant alcohol or sacrificial alcohol (i-PrOH).